The invention relates to pumps used to move a gas from one place or location (inlet) to another place or location (outlet) different from whence it came. In particular, the invention relates to rotary vane compressors and refrigeration systems using unloading compressors.
The main problem of controlling compression system capacity is to reduce both the capacity of the compressor and the power required to drive the compressor rotor to the same extent.
One commonly utilized means of achieving a capacity reduction is to bypass a portion of the fluid from the discharge side of the compressor back to the suction side. This method requires an auxiliary pipe connecting the discharge and suction sides of the compressor with a valve located in the pipe. Such an arrangement reduces the system capacity since a smaller amount of fluid is directed to the main system circuit, but it does not reduce the power consumption since the compressor pumps the same amount of fluid.
Another solution is to provide an auxiliary pipe, extending from the compressor outlet to an auxiliary inlet in the wall of the stator at a position where the rotor passes on its"" return travel from the outlet to the main inlet. This introduces pressurized gas into the re-expansion process of the compressor cycle, where the expanding gas imparts a driving force on the rotor. This reduces both the cooling capacity and power required to drive the compressor rotor. However, this arrangement requires modifying the profile of the stator wall in the re-expansion zone. This results in an impact on the compressor efficiency at regular mode. Also, it limits the controlled capacity range for each modified profile.
On the other hand, in many refrigeration or refrigerant compression applications, there are other times when it would be more desirable to have the ability to also achieve increased capacity. One way of achieving increased capacity is the inclusion of an economizer circuit into the refrigerant system. Typically, the economizer fluid is injected through an economizer port at a point after the compression chambers have been closed.
In one design, the system is provided with an unloader valve which selectively communicates the economizer injection line back to suction. In this arrangement, the fluid ports and passages necessary to achieve the economizer injection are also utilized to achieve suction bypass unloading, and thus the compressor and system design and construction are simplified. However, operating in regular mode, the compressor chamber communicates with the additional volume of the passages, thus impacting compressor efficiency. If the passages are made too small to reduce the impact on compressor efficiency, unloading capacity would not be enough.
As a further development a pulsed flow capacity control is achieved by rapidly cycling solenoid valves in the suction line, the economizer circuit, and in a bypass line with the percent of xe2x80x9copenxe2x80x9d time for the valve regulating the rate of flow. The provision of three modulating valves results in an increased complexity and a reduced reliability of the whole refrigeration system.
The present invention is directed to a method of reducing cooling capacity in a rotary vane compressor in such a way that the power requirement to drive the rotor is reduced to the same extent (or close to) as capacity is reduced. In an aspect of the invention this is accomplished without any impact on compressor efficiency at regular mode. In another aspect, this is accomplished without excessive complexity or low reliability.
The present invention provides for a rotary vane compressor comprising a rotor, a stator, and vanes placed in slots spaced apart about the rotor. The stator is provided with an inlet and an outlet and a compression region therebetween. The rotor rotates in a forward direction past the inlet through the compression region and then past the outlet thereby to transport gas from the inlet to the outlet. Two adjacent vanes, the rotor and a wall portion of the stator in the compression region define a compressor chamber. The stator is shaped to compress gas in the compressor chamber when gas travels from the inlet to the outlet. An economizer port is located in the compression region at a point where the port is in communication with the compression chamber after it has been closed for compression. A valve is associated with the economizer port, the valve body being formed from a part of the stator body. The seat of the valve in the closed position is shaped to be contiguous with the wall portion of the stator. The integrity of the whole compressor is maintained and compressor cycle efficiency is improved since there is no additional volume of passages attached to the compressor chamber and associated with the economizer port. In an opened position the valve provides communication between the compression chamber and the economizer port.
According to an aspect of the invention, when the valve is opened a part of the gas is returned back to the compressor inlet over an auxiliary passage between the economizer port and the compressor suction side. This reduces both potential cooling capacity and power required to drive the compressor rotor without impacting compressor efficiency at regular operating mode.
In yet another aspect of the invention there is provided a refrigeration system comprising a main circuit, and a bypass circuit. The main circuit comprises, in a closed loop, a compressor, a condenser unit, an expansion device, an evaporator unit, connecting piping and appropriate refrigeration control. The compressor includes a housing, an inlet, an outlet, a compression region therebetween, an economizer port located in the compression region at a point where the port is in communication with the compression chamber after it has been closed for compression, and a variable flow valve associated with the economizer port. A body of the valve is a part of a body of the housing and a seat of the valve in a closed position is shaped to be contiguous with internal portion of the housing. The bypass circuit has a second solenoid valve located between the economizer port and the suction side of the compressor. The variable flow valve, a control system, and a transducer, reading parameters associated with a system capacity demand, are wired in an electrical circuit. The control system activates the valves based on the capacity demand.
One more aspect of the invention there is provided a refrigeration system comprising a main circuit, and an economizer circuit. The main circuit comprises, in a closed loop, a compressor, a condenser unit, an expansion device, an evaporator unit, connecting piping and appropriate refrigeration control. The compressor includes a housing, an inlet, an outlet, a compression region therebetween, an economizer port located in the compression region at a point where the port is in communication with the compression chamber after it has been closed for compression, and a variable flow valve associated with the economizer port. A body of the valve is a part of a body of the housing and a seat of the valve in a closed position is shaped to be contiguous with internal portion of the housing. The economizer circuit includes a first solenoid valve, an additional expansion device and an economizing heat exchanger and is connected to the economizer port. The economizing heat exchanger provides thermal contact between refrigerant in the main circuit after the condenser unit and evaporating refrigerant in the economizer circuit after the additional expansion device. The variable flow valve, a control system, and a transducer, reading parameters associated with a system capacity demand, are wired in an electrical circuit. The control system activates the valves based on the capacity demand.
When the economizer and bypass circuits are applied together the refrigeration system includes a first solenoid valve in the bypass circuit and a second solenoid valve in the economizer circuit.
According to the invention the refrigeration system has an advantage in terms of the system simplicity and reliability since only one variable flow valve is required.